1. Technical Field of the Invention
This invention generally relates to the field of communication systems and, more particularly, to a method and apparatus for minimizing the effect of far-end cross-talk in a digital communication system.
2. Description of the Related Art
The speed at which digital communication systems provide users with information has grown over the years. The specific communication system used has evolved from a low data rate analog modem to the modern day high speed Digital Subscriber Line (xDSL) service. However, the physical transmission medium used to convey information to users has not changed. Typically, the transmission medium is “twisted pair” which is unshielded copper wires in close proximity to one another. Each twisted pair serves a respective user and is bundled with other twisted pairs, typically, in groups of 25 pairs.
Unfortunately, the proximity of each twisted pair to one another creates an impairment to transmitting information at a high speed. More specifically, when information is communicated on a twisted pair, the communication of that information interferes with communication on other twisted pairs. For instance, where you have a transmitting end of a circuit and multiple receiving ends, some or all of the receiving ends of the circuit can receive errors due to cross-talk from one interfering twisted pair in the bundle.
Cross-talk is especially problematic in high speed data transmission. Asymmetric Digital Subscriber Lines (ADSL), for example, offers data rates up to 8 Mb/s in the downstream direction (from the network to the home) and about one-eighth of this date rate in the upstream direction (from the home to the network). An even higher speed version of xDSL service is being developed known as Very-high-speed Digital Subscriber Lines (VDSL) that targets data rates up to about 50 Mb/s for the downstream channel. As xDSL systems provide greater speeds, the xDSL service becomes more susceptible to interferences such as cross-talk.
Most of the work in this area has focused on optimizing spectral shaping of the transmitted signal by taking into account the cable loss and cross-talk loss to maximize the signal-to-cross-talk ratio. Other cross-talk reduction methods focus on mitigating single user cross-talk. The single user cross-talk approach, however, treats cross-talk interference as colored stationary or cyclostationary noise. Other cross-talk reduction methods address the issue of multi-user detection, which treats multiple receivers as one entity and performs joint detection.
Unfortunately, conventional multi-user detection methods for xDSL applications are not practical because the users are physically separate from one another. Thus conventional methods can not adequately address the issue of multi-user cross-talk detection and correction where the users are physically separate from each other.